Machine for producing a triple-thread chain stitch for sewing webs over an edge

ABSTRACT

A triple-thread stitch is intended for sewing webs of netting over their edges, wherein one thread (2) forms straight loops (3) and two other threads (4 and 6) form turned loops (5 and 7). In the method of producing this triple-thread stitch, performed in a machine wherein the loop-forming members are the sewing needle (8), looper needle (9) and looper hook (10), the thread (6) of the looper hook (10) is formed into a turned loop (7) which is moved about the needle (8) until the latter&#39;s thread (4) forms a turned loop (5), and driven through the straight loop (3) of the thread (2) of the looper needle (9). In the machine for sewing netting webs over their edges with a triple-thread chain stitch, the looper hook (10) is mounted for moving about the needle (8) at the side of the device (17) for advancing the webs, which provides for forming from the thread ( 4) of the needle (8) a turned loop (5) when the looper hook (10) moves the turned loop (7) intermediate the needle (8) and its thread (4).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sewing technology, and moreparticularly it relates to a machine for producing triple-thread chainstitch for sewing webs over an edge.

2. Description of the Prior Art

There is known a triple-thread chain stitch, wherein the first thread ispositioned at one side of the webs being sewn and forms a series ofstraight loops parallel with the edge of the webs, and interweaves withthe second thread forming a similar series of loops at the other side ofthe webs, while the third thread forms straight overcasting or whiploops, each connecting two adjoining loops of one series and having itslegs received in one loop of the other series (cf. F. I. Chistyakov, A.M. Nikolaenko, "Sewing Machines", Moscow, MASHINOSTROJENIE Publishers,1976, p. 380). The knots formed by the interweaving of the first andsecond threads are disposed to one side of the webs, while the knotsproduced by the interweaving of the overcasting loops with the loops ofthe first and second threads are either disposed to the opposite sidesof the webs or so offset that a succession of these loops is situatedoutside the edges, at the borderline between the webs being sewn. Thelegs of the straight overcasting loops are running either parallel or ata small inclination toward each other.

A known method of producing such a triple-chain stitch, performed by asewing needle carrying the needle thread and by the first and secondloppers carrying, respectively, the first and second looper threads,includes the steps of:

piercing the webs with the needle, having pulled the needle thread inadvance through a loop of the first looper thread;

pulling the second looper thread through the loop of the needle thread,drawn through the webs;

pulling the first looper thread through the loop of the second looperthread; and

casting the loops thus produced in succession off the loopers andtightening the stitch.

However, experience of employing this stitch for sewing fishing nets hasrevealed insufficient strength of the produced seams, manifesting itselfin not unfrequent cases of mechanical damage of the fishing gear. Thedestructive effect of such damage is aggravated by the fact, when eitherone of the threads becomes broken, the chain stitch where all the threeseries of loops are straight readily loosens in the direction oppositeto that of its formation.

There is further known a triple-thread chain stitch for sewing up websover their edges, wherein the first thread forms a series of straightloops at one side of the webs being sewn, the second thread forms aseries of straight loops driven through the loops of the first threadand through the webs being sewn to their other side, and the thirdthread forms a series of turned loops with crossing legs which projectthrough the loops of the second thread and encompass the loops of thefirst thread (cf. SU Inventors' Certificate No. 820292; Int.Cl.³ D 05 B1/08, published July 30, 1983).

There is further known a method of producing such a triple-thread chainstitch for sewing webs, e.g. netting webs, over their edge, performed bysuccessively driving the needle thread through a loop of the looperneedle thread and through the webs, and subsequently driving a turnedloop of the looper hook thread, through the loop of the needle thread.This yields a triple-thread stitch including two series of straightloops and one series of turned loops with crossing legs.

This method is performed by a machine comprising a framework, means forguiding the webs into the sewing zone, means for retaining the sewn upedges of the webs, a device for advancing the webs and the main shaftoperatively connected with mechanisms for driving the needle mounted ona needle bar, the looper needle mounted on a rod and the hooper hookmounted in a cantilever fashion on a telescopic rotatable bar.

The telescopic rotatable bar having the looper hook mounted thereon in acantilever fashion extends above the horizontal needle bar, runningparallel therewith and belonging to one and the same plane. The looperhook in its extreme position overlies the needle at the outer side ofthe means for retaining the edges of the sewn webs, while the needle hasits eye for outlet of the sewing needle thread facing upwardly and isfreely received in the gap between the means guiding the webs into thesewing zone and means for retaining the sewn up edges of the webs.

The tip of the looper hook which is in the form of a straight hollowstem is upwardly pointed. The guiding cam of the mechanism driving thelooper hook is in the form of a cylindrical disk with a valley smoothlyconjugating with the cylindrical surface of the disk.

Owing to the turned loops, the third thread of a chain stitch of thistype is somewhat better linked with the second thread. If the thirdthread is broken, its turned loops tend to tighten on the loops of thethird thread, thus restraining to a certain degree the loosening of thechain stitch. This amounts to definite advantages of a stitch of thistype over the first-mentioned stitch, and therefore netting webs joinedby this stitch have become broadly used in the production of industrialfishing gear.

However, in this stitch, too, the knots connecting the first thread(needle thread) with the second and third threads (looper needle andlooper hook threads, respectively) are formed exclusively by theinterweaving of straight loops. Therefore, when either the first threador the second one becomes broken, the chain stitch loosens as readily asin the first-described case. Furthermore, the turned loops of the thirdthread, interconnecting the pairs of adjacent straight loops of thesecond thread, are uncommonly large and would not be made smaller onaccount of the very structure of the seam, whereby the turned loops areall but similar to straight loops, and, consequently, inadequatelyeffective because when the third thread becomes broken, they tighten butin some cases, and in most cases become spread giving rise toself-loosening of the seam. Thus, to prevent self-loosening of atriple-thread chain stitch of this structure used for sewing up nettingwebs intended for industrial fishing gear, a seam thus formed isstitched at certain intervals with an additional second seam producedmanually in intermittent stitches superimposed from above upon the mainseam, which steps up the input of labour into the manufacture of thefishing gear.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a machine capable ofproducing a triple-thread chain stitch for sewing webs over their edgeswherein the loops formed are so interwoven as to provide for aloosening-proof seam upon breakage of one, two or all the three threads,thus avoiding the necessity of making an additional safety seam andallowing a step up in the productivity of operation of sewing up webs,e.g. netting webs.

This object is attained in connection with a triple-thread chain stitchfor sewing webs over their edges, wherein one thread forms a series ofstraight loops at one side of the webs being sewn, the second threadforms a series of loops driven through the loops of the first thread andthrough the webs being sewn to their other side, and the third threadforms a series of turned loops with crossing legs, introduced throughthe loops of the second thread and encompassing the loops of the firstthread, in which stitch, in accordance with the invention, the loops ofthe second thread are also turned, their legs crossing each other.

In the method of producing a triple-thread chain stitch for sewing websover their edges, including the successive steps of driving the needlethread through a loop of the looper needle thread and through the webs,and subsequently driving a turned loop of the looper hook thread througha loop of the needle thread, in accordance with the invention, prior todriving the turned loop of the looper hook thread through the loop ofthe needle thread, the latter is moved about the needle to form from theneedle thread a turned loop with crossing legs.

The disclosed structure of a triple-thread chain stitch and the methodof producing it in accordance with the invention provide for aloosening-proof seam when either a single one of the threads or all thethree threads become broken. Moreover, there is precluded theeventuality of either one of the three threads being accidentally pulledout, resulting in the formation of crimples in the seam, adverselyaffecting the operability of sewn items. This has been attained owing tothe turned needle thread loops in the stitches of the seam, driventhrough the sewn-up webs, being narrow and closely hugging the crossinglegs of the turned loops of the looper hook thread along practicallytheir entire perimeters. Thus, when either one of the sewing threads iseither broken or pulled out from the seam, the turned needle threadloops tighten on the turned loops of the looper hook thread,safeguarding each other from self-loosening and firmly holding the loopsof the looper hook thread, so that the seam would not become loose.

When fishing netting is manufactured, this allows doing withoutsuperimposing upon the triple-thread stitches of the seam joiningnetting webs an additional intermittent safety seam made manually toprevent self-loosening of the main seam, which, in its turn, providesfor stepping up the labour productivity, reducing the input of sewingthread and enhancing the performance properties of sewn articles.

A machine capable of performing the disclosed method comprises aframework having mounted thereon means for guiding webs into the sewingzone, means for retaining the sewn up edges of the webs, a device foradvancing the webs and a main shaft operatively connected withmechanisms for driving the needle mounted on the needle bar. The looperneedle is mounted on its rod and the looper hook mounted in a cantileverfashion on a telescopic rotatable bar. In accordance with the presentinvention, the looper hook is mounted for moving about the needle at theside of the device for advancing the webs, its telescopic rotatable barbeing offset from the needle bar towards the device for advancing thewebs and inclined to an imaginary plane including the axis of the needleand the line of stitching the edges of the webs, the needle being somounted in the needle bar that its eye faces the device for advancingthe webs, a groove being made in the needle at the same side behind theeye.

It is expedient that the inclination angle of the telescopic rotatablebar of the looper hook be within 5°-15°, and the extent by which thetelescopic rotatable bar of the looper hook is offset relative to theneedle bar be within one half of the length of the working portion ofthe looper hook.

With the machine having the disclosed structure, it is possible toperform the method of forming a loosening-proof triple-thread chainstitch by turning the loop of the needle thread prior to having theturned loop of the looper hook thread introduced thereinto.

It is possible to provide under the needle, intermediate the means forguiding the webs and the looper hook, an abutment for the needle thread,mounted on the means for retaining the sewn up edges, so as to ensurethe necessary conditions for uniform tensioning of the loops of thelooper needle thread and looper hook thread at the moment of theformation of a turned loop of the needle thread.

The working portion of the looper hook is preferably saddle-shaped witha tip bent downward, and the tip preferably has a share-shaped slope atan angle in a 20°-30°range, the eye of the looper hook for the outlet ofthe thread being preferably below the share-shaped slope at its outerside.

The bent tip of the looper thread provides for reliable engagement ofthe needle thread as it is pulled downwardly to underlie the needle atthe moment of forming a turned loop of the needle thread and introducinginto this turned loop through a turned loop of the looper hook thread.Upon the looper needle having engaged the turned loop of the looper hookthread, the looper hook readily casts off the turned loop of the needlethread owing to the saddle-like shape of its working portion. Theplough-share-shape of the tip and the eye for the outlet of the looperhook thread being arranged under this tip provide for reliable passageof the looper hook over its own thread as the looper hook moves from theinner side of the webs being sewn to their outer side, precluding anywrapping of this thread about the working portion of the looper hook andeventual missing of its loop, thus enhancing the reliability of thechain stitch formation.

It is also expedient for the looper hook to have a longitudinal grooveabove its eye, adapted to receive therein the looper hook thread as thelooper hook engages the loop of the needle thread, for this loop toslide easily onto the working portion of the looper hook.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in connection with examples offormation of a triple-thread chain stitch for sewing webs over theiradges and of a method of producing this stitch, and of an embodiment ofa machine for performing this method, with reference being made to theaccompanying drawings, wherein:

FIG. 1 is a schematic developed view of a triple-thread chain stitch inaccordance with the invention;

FIGS. 2 to 8 illustrate the succession of operations of forming thetriple-thread chain stitch shown in FIG. 1;

FIG. 9 schematically illustrates a mechanical diagram of a machine forperforming the disclosed method of forming a triple-thread chain stitchfor sewing webs over their edges;

FIG. 10 illustrates the relative arrangement of the looping mechanisms,corresponding to the initial or home position of the looper hook;

FIG. 11 schematically shows a side view of the relative arrangement ofthe needle, looper needle and looper hook, with the looper hook being inits fully extended position;

FIG. 12 shows the relative arrangement of the needle, looper needle,looper hook and abutment for the needle thread, viewed from the front;

FIG. 13 is a sectional view taken on line XIII--XIII of FIG. 12; and

FIG. 14 shows the actuating cam of the machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrated in FIG. 1 is a segment of a triple-thread chain stitch forsewing webs 1 over their edges in accordance with the invention, shownin a developed view. In the stitch, one of the threads--the thread2--forms a series of straight loops 3 at one side of the webs 1 beingsewn (it is at this series of loops that the view has been developed).The second thread 4 forms a series of turned loops 5 with crossing legs,introduced through the loops 3 of the first thread 2 and through thewebs 1 being sewn to their other side. The third thread 6 forms a seriesof turned loops 7 with crossing legs, introduced through the turnedloops 5 of the second thread 4 and encompassing the loops 3 of the firstthread 2.

The method of forming a triple-thread chain stitch in accordance withthe invention includes the following steps.

The stitch is formed with the aid of a sewing needle 8 (FIG. 2) carryingthe thread 4, a looper needle 9 and a looper hook 10 carrying,respectively, the threads 2 and 6. The looper needle 9 is operated toform the loop 3 of the thread 2, disposed to one side of the webs 1being sewn along the stitching line. The needle 8 is operated tosuccessively introduce the thread 4 through the loop 3 of the thread 2and through the webs 1 to their other side. The looper hook 10 islowered upon the thread 4 and operated to drive this thread 4 tounderlie the needle 8, at the same time turning the loop 5 formed of thethread 4. Then the looper hook 10 is introduced into the turned loop 5of the needle thread 4, with the looper hook underlying the needle 8 andthe thread 4 of the needle 8 underlying the looper hook 10 (FIG. 3). Atthe same time the looper needle 9 is driven upwardly, to form the loop 3of the thread 2 on the needle 8. The previously formed preceding turnedloop 7 of the thread 6 is retained by the looper needle 9. It is on thecrossed legs of this loop 7 of the thread 6 that the closing of thepreceding turned loop 5 of the needle thread 4 is commenced. Then theneedle 8 is retracted backwardly, and at the same time the looper hook10 moves about the point of the needle 8 in the upward direction (FIG.4).

The successive turned loop 5 of the thread 4 formed during the returnstroke of the needle 8 is carried over the sewn edges 11 of the webs 1,e.g. netting webs, to their other side by the looper hook 10 (FIG. 5),the edges 11 being conditionally showed in FIGS. 2 to 8 asthree-dimensional square bodies for clarity sake. Meanwhile, thepreceding turned loop 5 of the thread 4 is closed, its legs crossingeach other. The loop 3 of the thread 2 is cast off the needle 8 andmoves onto the thread 4 pulled by this needle 8. The turned loop 7 ofthe thread 6 of the looper hook 10 is cast off the looper needle 9 andpasses onto the vertical legs of the loop 3 of the thread 2,encompassing them at their upper portion. The newly formed loop 5 of thethread 4 is thus introduced through the loop 3 of the thread 2. Thethread 6 tensioned by the looper hook 10 finally forms its turned loop7, crossing its legs. At the same time, the crossed legs of thepreceding loop 5 of the thread 4 are finally tightened.

Simultaneously with the formation of the turned loop 7 of the thread 6and the final turning and tightening of the crossed legs of thepreceding loop 5 of the thread 4, there takes place the final tighteningof the already formed preceding stitch. This is assisted by the advanceof the netting webs 1 being sewn, effected when the needle 8 isretracted from the engagement with the webs 1.

The looper hook 10 is moved under the looper needle 9 (FIG. 6). Then thelooper needle 9 is moved downward and introduced between the looper hook10 and its thread 6. The thread 2 of the looper needle 9 overlies thelooper hook 10, while the webs 1 being sewn are still fed forwardthrough the length of a stitch. Upon the looper needle 9 having engagedthe successive loop 7 of the thread 6, the looper hook 10 is retractedto the right (in the drawing), with the newly-formed loop of the thread6 of the looper hook 10 being held by the looper needle 9, the precedingturned loop of the thread 6 of the looper hook 10 and the straight loop3 of the thread 2 being tightened (FIG. 7). The stitch 12interconnecting the preceding and newly-formed loops 3 of the thread 2and the turned loop 5 of the thread 4 are meanwhile retained on themoving leg of the newly-formed loop 7 of the thread 6 which is carriedby the looper hook 10 over the edges of the webs 1 being sewn in thedirection of the working stroke of the needle 8 (FIG. 8). The looperneedle 9 with its thread 2 is introduced deeper into the loop 7 of thethread 6 of the looper hook 10, while the needle 8 with its thread 4 ismoved between the looper needle 9 and its thread 2, subsequentlypiercing the webs 1 being sewn. Then the abovedescribed succession ofsteps is repeated.

The machine for performing the abovedescribed method comprises aframework 13 (FIG. 9) having mounted thereon means 14 for guiding thewebs 1 into the sewing zone 15 (i.e. into the zone of the arrangementand three-dimensional motion of the loop-forming members: the sewingneedle 8, looper hook 10 and looper needle 9), means 16 for retainingthe sewn up edges of the webs 1, a device 17 for advancing the webs 1,and the main shaft 18 of the machine, operatively connected withmechanisms 19, 20, 21, respectively, for driving the sewing needle 8,looper needle 9 and looper hook 10.

The means 14 for guiding the webs 1 into the sewing zone 15 is mountedon the framework 13 on a bracket 22 and includes a wall 23, a lip 24 anda crosspiece 25 joining them perpendicularly.

The means 16 for retaining the sewn up edges 11 of the webs 1 is in theform of an inverted U-shaped channel member situated behind theweb-guiding means 14 in the direction of the advance of the webs 1,defining therebetween the sewing zone 15. The means 16 for retaining thesewn up edges 11 is provided on the outside with an abutment 26 for thethread 4 of the sewing needle 8. The abutment 26 underlies the needle 8and encompasses the needle 8 at the side of the web-guiding means 14.

The device 17 for advancing the webs 1 includes a driven toothed disk27, a hanger 28 with two spring-urged weight rollers 29 mounted on acommon axle 30, and an eccentric 31 with a driver. The toothed disk 27is operatively connected through an overrunning clutch 32 mounted on theaxle 33 of a connecting-rod 34 with the spherical joints 35 of a bellcrank 36, and through a strap 37 with an eccentric 38 on the main shaft18. By varying the length of the corresponding arm of the bell crank 36connected with the spherical joint 35 the stitch length in a seam can beadjusted.

The mechanism 19 for driving the sewing needle 8 includes a needle bar39 mounted perpendicularly to the wall 23 of the means 14 for guidingthe webs 1 into the sewing zone 15, associated with a frame 40, and anaccentric 41 fast on the main shaft 18, received in the frame 40 forengagement therewith. The needle bar 39 carries a holder 42 in which theneedle 8 is releasably secured. The needle 8 has made therein an eye 43for the thread 4 and a groove 44 for the passage of the looper hook 10,made intermediate the eye 43 and holder 42 at the side of the eye 43.The needle 8 is secured in the holder holder 42 for its eye 43 to facethe web-advancing device 17.

The mechanism 20 for driving the looper needle 9 includes a rod 45mounted for reciprocation in a guide frame 46, a link 47, a rocker arm48 and a strap 49 pivotally connected to one another. The main shaft 18carries an eccentric 50 received in the strap 49. The rod 45 has securedtherein the looper needle 9 having a projection or lug 51 (FIGS 10 and11) for guiding the thread 2 normally from the looper needle 9 towardsthe means 16 for retaining the sewn-up edges 11.

The mechanism 21 for driving the looper hook 10 includes a rod 52 with akey 53 and a tubular guide 54 with a keyway slit 55, defining jointly arotatable telescopic bar, a transverse arm 56 with a follower 57 mountedon the tubular guide 54, and an intermediate arm 58 carrying a follower59 engaging a cam 60 fast with the main shaft 18. The tubular guide 54further supports an adjustment washer 61, a sleeve 62 mounted with theaid of a pivot 63 on a bracket 64 of the machine, and spring 65interconnecting the adjustment washer 61 and the sleeve 62. The sleeve62 has a port 66 made therethrough for rotation of the transverse arm56. The rod 52 supports a movable sleeve 67, pivotally connected withthe aid of a transverse pivot 68, through the fork 69 of a rocker arm 70and a connecting-rod 71 to a crank 72 made integral with the drivingpulley of the machine, fast on the main shaft 18. Lock washers 73 atboth ends of the sleeve 67 retain it against longitudinal displacementon the rod 52.

The rod 52 carries a holder 74 wherein the looper hook 10 is secured ina cantilever fashion for moving about the sewing needle 8 at the side ofthe web-advancing device 17 (FIG. 9). The telescopic rotatable bar madeof the rod 52 and its tubular guide 54 is offset relative to the needlebar 39 in the direction towards the web-advancing device 17, and isinclined with respect to an imaginary plane A (FIG. 10) including theaxis a--a of the needle 8 and the line b--b of stitching the edges 11 ofthe webs 1, at an angle α equalling 5°-15°, whereas the distance "1"(FIG. 12) through which the telescopic rotatable bar of the looper hook10 is offset relative to the needle bar 39 is selected so as not toexceed one half of the length of the working portion 75 of the looperhook 10. The angle α equalling 5°-15° is selected so that the looperhook 10 in its initial or home position behind the looper needle 9should be above the needle 8, and in its position on the outside of theweb-guiding means 14 below the needle 8.

The extent "l" of the offset of the bar of the looper hook 10 relativeto the needle bar 39 is selected so that the looper hook should rotatealternatingly through identical angles about a vertical line includingits axis of rotation, to provide optimized conditions for both takingand casting off the loop 5 of the thread 4.

For easier sliding of the loop 5 of the thread 4 along the workingportion 75 of the looper hook 10, the portion 75 is saddle-shaped,reproducing the arc along which the looper hook 10 rotates about theaxis of the telescopic bar. The tip 76 of the looper hook 10 is bentdownwardly and has a slope 77 at an angle β to the bottom generatrix ofthe tip, equalling 20°-30°.

The value of the angle β in the 20° to 30° range is selected so that theedge of the slope 77 of the downwardly bent tip 76 of the looper hook 10should be either at the level of or slightly above the eye 78 for thethread 6, so that the thread 6 should pass below the looper hook 10 andnot become wrapped about its working portion 75 as the looper hook 10 ismoved to the outer side of the sewn webs 1, i.e. towards the workingrath of the sewing needle 8.

The thread eye 78 of the looper hook 10 is situated intermediate itsworking portion 75 and its downwardly bent tip 76, behind the slope 77at its bottom part. The looper hook 10 further has a groove 79 (FIG. 13)running longitudinally in its working portion 75 above the eye 78.

The cam 60 is in the form of a disk with two opposed concentric arcs 80and 81, the radius of the arc 80 being greater than the radius of thearc 81, and the difference between these radii being selected so thatthe looper hook 10 driven through its working stroke should be able toenter the turned loop 5 of the thread 4 by its working portion 75, andturn through an angle sufficient for casting off the loop 5 in its homeposition.

The arcs 80 and 81 merge through smooth transition fields 82, one of thetransition fields 82, as it can be seen in FIG. 14, being more steep tocorrespond to the position of casting the loop 5 formed of the thread 4of the needle 8 off the looper hook 10, and the other field 82 slopingmore gently to correspond to the position of engaging the successiveloop 5 of the thread 4 as it is being formed.

The machine has three thread guides 83 (FIG. 9) associated withcorresponding devices 84 for adjusting the tension, respectively, of thethread 4 supplied to the sewing needle 8, the thread 2 supplied to thelooper needle 9, and the thread 6 supplied to the looper hook 10.

The sewing needle 8 has a notch 85 at its base for the passage of thelooper needle 9 at the side opposite to the groove 44.

The machine operates, as follows.

The three threads 2, 4, 6 (or ropes, depending on the type of thenetting webs to be sewn) are threaded through the machine from theirrespective three supply bobbins or spools. The threads are guided,first, through the respective tension adjustment devices 84 and threadguides 83, and then the thread 4 is guided through the sewing needle 8,the thread 2 through the looper needle 9, and the thread 6 through thelooper hook 10. Then the ends of the thus guided three threads arepulled out, brought together, guided under the means 16 for retainingthe sewn edges 11 of the webs 1 and about the rim of the toothed disk 27of the web-advancing device 17, and urged thereto by the weight rollers29, by releasing the springurged hanger 28 with the aid of the eccentric31.

Removable straps--either of thread or of rope--tied to the endmost edgecells of the netting webs 1 to be sewn are used to guide the webs 1between the wall 23 and lip 24 into the sewing zone, and set themproperly with respect to the cross-piece 25. Then the ends of theremovable straps, same as the ends of the threads in the previous step,are put between the rim of the toothed disk 27 and the weight rollers29, by first withdrawing the rollers 29 slightly from the toothed disk27, with the aid of the eccentric 31 and then returning them into theurging position.

The number of the rows of cells of the netting webs 1 to be sewn,selected for forming a seam, is adjusted and set by moving the means 14for guiding the webs 1 into the sewing zone 15 relative to the sewingneedle 8. A required pitch of advancing the webs is set in a knownmanner by varying the working length of the lower arm of the bell crank36.

With the machine turned on, the main shaft 18 is set in motion to drivethe mechanisms 19, 20, 21 actuating, respectively, the sewing needle 8,looper needle 9 and looper hook 10, and also the web-advancing device17.

The interaction of the respective mechanisms 19, 20, 21 driving thesewing needle 8, looper needle 9 and looper hook 10 results in straightopen loops 3 (FIG. 1) of the thread 2 supplied to the looper needle 9being interwoven, same as the turned closed loops with crossing legs ofthe thread 4 supplied to the sewing needle 8, and the turned closedloops 7 with crossing legs of the thread 6 supplied to the looper hook10, forming a triple-thread chain stitch seam. The loops 3 of the thread2 are situated at one side of the webs 1 being sewn, the loops 5 of thethread 4 are passed through the cells of the webs 1, and the loops 7 ofthe thread 6 pass above and over the edges 11 of the webs 1 being sewn,overcasting them from above.

As the bell crank 36 is rocked by the eccentric strap 37, the tootheddisk 17 is intermittently unidirectionally rotated through theoverrunning clutch 32 through angular steps corresponding to therequired pitch of the seam, advancing the sewing threads and the webs 1by extents corresponding to successive stitches.

The moment the toothed disk 27 is arrested and the webs 1 haltcorrespondingly, the looper needle 9 moves down in a vertical planesituated at the inner side of the webs 1 being sewn, parallel with theirdirection of advance (FIG. 7). The needle 8 which is likewise positionedat the inner side of the webs 1 is driven through its working stroke,entering first the straight open loop 3 of the thread 2 formed by thedownward motion of the looper needle 9, passing through the turned loop7 of the thread 6 of the looper hook 10, and then piercing the webs 1being sewn, guiding its thread 4 to their outer side. As the needle 8appears at the outer side of the webs 1, the looper hook 10 moves abovetheir sewn up edges 11 from the inner to outer side of the webs 1 (FIG.2), plunges its tip 76 into the groove 44 of the sewing needle 8,situated behind the latter's eye 43, and leans upon the thread 4 to pullit down to underlie the needle 8. The turned closed loop 7 of the thread6 of the looper hook 10, extending through the preceding tuened closedloop 5 of the thread 4, is retained in the meantime by the looper needle9, engaging one leg of the loop 3 of the thread 2 and the looper needle9 above the sewing needle 8 and its thread 4.

Still moving downwardly, the looper hook 10 rotates about thelongitudinal axis of the telescopic bar made of the movable rod 52 andits tubular guide 54 and is driven by the cam 60 to enter the spacebetween the needle 8 and its thread 4, the latter underlying the workingportion 75 of the looper hook 10 (FIG. 3). At the same time, the looperneedle 9 returns to its up position, its lug passing through the notch85 in the sewing needle 8, and casts off the turned loop 7 of the thread6, which passes onto both vertical legs of the loop 3 of the thread 2retained by the needle 8. Thus, the sewing needle 8 is now inside theloop 3 of the thread 2, with the loop 7 of the thread 6 overlying theloop 3.

The moment the sewing needle 8 starts retreating from its fully extendedworking position, the looper hook 10 moves up, its working portion 75passing about the point of the needle 8 (FIG. 4). The turned loop 5 ofthe thread 4 is formed on the working portion 75 of the looper hook 10,which is carried over the sewn up edges 11 of the webs 1 to their innerside (FIG. 5). The needle 8 moves out of engagement with the webs 1which start advancing under the pull of the toothed disk 27. Thestraight open loop 3 of the thread 2 of the looper needle 9 is cast offthe sewing needle 8 and passes onto the thread 4 pulled by the needle 8.The thread 6 pulled by the looper hook 10 forms its successive turnedclosed loop 7, crossing its legs. At the same time, the preceding loop 5of the thread 4 is turned and finally closed by its legs becoming fullycrossed, and the preceding fully formed stitch is finally tightened.This operation is supported by the advancing step of the webs 1.

As the mechanisms 19, 20, 21 continue their driving action, the looperhook passes by the concave part of its working portion 75 under thelooper needle 9 beyond the vertical path of its travel (FIGS. 6). Thelooper needle 9 moves down, entering the space between the workingportion 75 of the looper hook 10 and its thread 6. The thread 2 of thelooper needle 9 now overlies the working portion 75 of the looper hook10 by the stretch 12 of which one end passes through the eye of thelooper needle 9 and the other end enters from above the formed precedingturned closed loop 7 of the thread 6. The webs 1 are meanwhile beingadvanced by the toothed disk 27, and the sewing needle 8 begins itsworking stroke.

Upon the looper needle 9 having engaged the loop 7 of the thread 6 ofthe looper hook 10, the latter is retracted from the looper needle 9 tothe right (in the drawing), i.e. in the advancing direction of the webs1 being sewn, owing to the transverse arm 56 of the telescopic barmoving from the greater-radius arc 80 (FIG. 14) of the cam 60 onto itssmaller-radium arc 81.

The newly formed loop 7 (FIG. 7) of the thread 6 of the looper hook 10is retained by the looper needle 9, while the preceding turned loop 7 ofthe thread 6 and loop 3 of the thread 2 of the looper needle 9 arefinally tightened.

The stretch 12 of the thread 2 of the looper needle 9 and the loop 5 ofthe thread 4 are held on the moving leg of the newly formed loop 7 ofthe thread 6 being carried by the looper hook 10 over the edges 11 ofthe webs 1 in the direction of the working path of the needle 8 (FIG.8). The looper needle 9 with its thread 2 moves still further into theloop 7 of the thread 6. The sewing needle 8 with its thread 4 enters thespace between the looper needle 9, the thread 2 and the edges 11 of thewebs 1, piercing subsequently the row of cells being stitched. Thetoothed disk 27 now halts, and the advancing step of the webs 1 beingsewn is discontinued. The tip 76 of the looper hook 10 approaches thegroove 44 of the needle 8, above the thread 4 extending from the eye 43of the needle 8.

The abovedescribed sequence of operations of making successive stitchesis then repeated.

The herein disclosed machine with a horizontally arranged sewing needleprovides for sewing netting webs in a vertical position. It should beclearly understood, however, that the abovedescribed principle ofoperation and formation of a chain stitch can be implemented in amachine with a different (e.g. vertical) arrangement of the sewingneedle, with the disclosed relative arrangement and interaction of thesewing needle, loopers and the line of advance of netting webs beingsubstantially retained.

In this, the driving linkages of the mechanisms actuating the needle andloopers can be turned accordingly to achieve a better layout of theunits of the sewing machine.

Other modifications and changes are possible without departing from thespirit and scope of the invention, as set forth in the claims to follow.

The invention can be used to the utmost effect for sewing webs offishing nets in the manufacture of trawls, purse seines and otherindustrial fishing gear and implements, as well as for sewing webs ofbag netting.

I claim:
 1. A triple-thread stitching machine for sewing webs over theiredges, comprising a framework (13) having mounted thereon means (14) forguiding the webs into a sewing zone; retaining means (16) for retainingthe sewn up edges of the webs; a device (17) for advancing the webs anda main shaft (18) operatively connected with mechanisms (19, 20, 21),respectively, for driving a sewing needle (8) mounted on a needle bar(39), a looper needle (9) mounted on an associated rod (45) and a looperhook (10) mounted in a canti-lever fashion on a telescopic rotatablebar, the looper hook (10) being mounted for moving about the needle (8)at the side of the device (17) for advancing the webs, the telescopicrotatable bar being offset from the needle bar (39) towards the device(17) for advancing the webs and inclined with respect to an imaginaryplane including the axis of the needle (8) and the line of stitchingthrough the edges of the webs, the needle (8) having an eye (43) andbeing so mounted in the needle bar (39) that its eye (43) faces thedevice (17) for advancing the webs, and the needle (8) having a groove(44) made therein at the same side thereof, behind the eye (43).
 2. Amachine as claimed in claim 1, wherein the angle of inclination of thetelescopic rotatable bar of the looper hook is in a range from 5° to15°, and the extent (l) by which the telescopic rotatable bar of thelooper hook (10) is offset relative to the needle bar (39) is selectedto be within one half of the length of the working portion (75) of thelooper hook (10).
 3. A machine as claimed in claim 1, comprising anabutment (26) for the needle thread, situated under the needle (8)intermediate the means (14) for guiding the webs and the looper hook(10) mounted on the means (16) for retaining the sewn up edges.
 4. Amachine as defined in claim 2, wherein the working portion (75) of thelooper hook (10) is saddle-shaped with a tip (76) bent downward, the tiphaving a slope (77) at an angle in a 20° to 30° range, the eye (78) ofthe looper hook for the outlet of the thread therefrom being below theslope (77), at the outer side thereof.
 5. A machine as claimed in claim4, wherein the looper hook (10) has an elongated groove (79) above itseye (78).